The present application claims the benefit of French patent application 99 14619 filed Nov. 22, 1999, the disclosure of which is hereby incorporated by reference.
(I) Field of the Invention
The present invention relates to the field of the treatment with ozone of liquids, which treatment with ozone perhaps, as is known, is used in a very large number of industrial applications: for example in connection with the environment (water and effluent treatment, and the like), in the treatment of foodstuffs with ozone (liquid foods, in particular drinks, washing foodstuffs with ozonized water, such as seafood or also fruit and vegetables) or in aquaculture and pisciculture (rearing sites or all or part of the water which feeds the rearing pond or ponds of the user site is treated with ozone).
(II) Description of the Related Art
The treatment of piscicultural or aquacultural rearing sites with ozone has formed the subject of very extensive literature. Reference can be made, for example, to French Patent Application on behalf of Applicant Company FR-99 06567, which is concerned with the ozonization of rearing sites operating in closed circuits. The literature emphasizes the considerable advantage in treating water which feeds the ponds (health advantages, productivity, and the like). It is nevertheless a fact that difficulties and questions remain relating to the use of ozonization, treatments. These difficulties and questions are related in particular to the fact that the residual oxidizing components of a treatment with ozone may be toxic to the farmed species, whether it is the residual ozone itself in the medium or all the oxidizing by-products originating from the ozonization reactions of ozone with the medium (in particular salts, in the case of seawater).
It is also necessary to take into consideration the fact that, when ozone is injected into water (or any other liquid), part of this ozone is immediately consumed by the water in attacking organic matter, such as colors or bacteria, or in reactions with salts present in the water. Only subsequent to such consumption does the injection of ozone actually give rise to an ozone or oxidant residue which can be taken into account in carrying out the treatment targeted by the application under consideration.
The targeted treatment can, of course, be highly variable, depending on the application under consideration and depending on the specifications pursued by each user site. The treatment carries out one or more actions from the following actions: bleaching, disinfection, deodorization or water purification of the water (removal of toxic or undesirable components).
A person skilled in the art commonly speaks, with regard to this immediate consumption of ozone by the water (or by the liquid in the case of the most general application), of xe2x80x9cozone demandxe2x80x9d of the water under consideration.
In what follows, reference is made to the case of the treatment of a water while keeping in mind the fact that these treatments (and the notion of xe2x80x9cozone demandxe2x80x9d which is associated) applies more generally to liquids of highly varied origins.
It may therefore be said, with regard to this xe2x80x9cozone demandxe2x80x9d of the water to be treated:
that this demand represents the amount of ozone immediately consumed (it may even be said xe2x80x9cswallowedxe2x80x9d) by the water;
in other words, this xe2x80x9cozone demandxe2x80x9d is the amount of ozone which can be introduced into the water before the appearance of a residue (of ozone and/or of oxidant) in the water;
it depends on the quality of the water to be treated;
the determination of this ozone demand of the water to be treated and of the persistence of the resulting oxidant or ozone residue makes it possible to calculate the ozone treatment dose to be applied to the water under consideration.
The level of treatment to be applied to the water under consideration will therefore be determined as a function:
of the oxidant or dissolved ozone residue to be maintained in the water after having satisfied the instantaneous demand of the water under consideration, in other words of the effectiveness desired according to the treatment under consideration (for example, amount starting from which the desired disinfecting effect is effectively obtained);
of the safety of the site of use under consideration (local legislation or alternatively, for example, in the context of fish farms not tolerating any oxidants and/or ozone residue beyond a given residence time xcex94T).
The literature records a number of existing solutions for the determination of the ozone demand of a water to be treated, which solutions will be described in more detail in the context of FIGS. 1 and 2 hereinbelow, FIG. 1 being devoted to a determination solution which may be described as a xe2x80x9cbatchxe2x80x9d-style solution, whereas FIG. 2 is devoted to a determination solution which may be described as a xe2x80x9ccontinuousxe2x80x9d determination.
According to the first prior method for determination of the ozone demand of a water to be treated, a gas with a predetermined ozone content is injected into a sample of the water to be treated, the water sample is stirred and then, on the one hand, the dissolved ozone content of the water is determined and, on the other hand, the ozone content of the gas phase lying above the liquid water phase in the sample is determined.
The ozone demand is then determined by a conventional conservation equation relating to the initial amount of ozone injected through the gas, the dissolved ozone content of the water after stirring and the gaseous ozone content of the as phase existing above the liquid phase of the sample.
The disadvantages of such a xe2x80x9cbatchxe2x80x9d-style determination method are related in particular to the accuracy necessary in knowing the ozone content of the ozonized gas introduced but also to the fact that, in order to quantitatively determine the sample (in its liquid phase and in its gas phase), it is necessary to withdraw liquid and gas, which already per se (in the fact of withdrawing alone) falsifies the result of the measurement since ozone then naturally escapes from the liquid medium.
According now to the second so-called xe2x80x9ccontinuousxe2x80x9d determination method, the water to be treated, on the one hand, and an ozonized gas, on the other hand, are delivered to a contactor of continuous bubble column type in order to carry out dissolution in the contactor, so as to analyze, at the outlet of the contactor, the water and its dissolved ozone residue, and the non-transferred ozonized gas (outlet gas).
It is then seen that this continuous determination method is certainly reliable and furthermore widely used in the literature but unquestionably exhibits the disadvantage of requiring a large volume of water to achieve equilibrium and also the use of a great deal of equipment (numerous analyzers), therefore being relatively complex and not very compact.
A particular object of the present invention is to solve the abovementioned technical problems in connection with the determination methods according to the prior art.
The method according to the invention for the determination of a level of treatment (T) with ozone of a liquid to be treated then comprises the implementation of the following measures:
a) there is available a store of the liquid to be treated, the initial dissolved oxidants and/or ozone content of which is Ci,
b) an ozonized water mother solution with a given and constant volume of dissolved ozone Cm is manufactured (starting from distilled or demineralized water);
c) a volume Vm of the mother solution is withdrawn in order to introduce it into a sample of the store with a volume of Vi;
d) the content Cf of residual oxidant and/or dissolved ozone in the sample after the addition of Vm is measured, immediately after addition and/or at predetermined (regular or irregular) time intervals after the addition;
e) the level of treatment to be applied to the liquid is determined as function of the value of the quantity Ci-Cf (thus, as will have been understood, as a function of the difference between the amount of residual oxidants and ozone present in the sample after addition and that initially present in the sample before addition).
As will be clearly apparent to a person skilled in the art, the ozonized water mother solution, in order to be xe2x80x9cwith a given and constant content of dissolved ozone,xe2x80x9d will advantageously be obtained at saturation (this being in order to avoid as far as possible self-decomposition phenomena): the saturation of a liquid with a dissolved gas, in this instance ozone, being, as is known, according to Henry""s law, a function of the nature of the liquid and of the temperature but also of the partial ozone pressure in the injected gas.
According to one of the embodiments of the invention, the liquid to be treated is a fresh water and the level of treatment T is determined in the following way:
the ozone consumption of the water is evaluated by the expression:
Consumption=CmVm+CiVixe2x88x92Cf(Vm+Vi) in mg;
the ozone demand of the water to be treated is deduced therefrom by the following expression: ozone demand=consumption/Vi in mg/l;
a level of treatment T greater than the value of the ozone demand is chosen.
As will be clearly apparent to a person skilled in the art on reading all the above, the level of treatment T greater than the value of the ozone demand will be chosen as a function of each final application and therefore, according to the situation, as a function of the residue desired by the user site and as a function of the persistence of ozone and/or of oxidant in the water to be treated for various residence times (see stage d) above).
According to one of the embodiments of the method in the case of such a fresh water, the level of treatment T greater than the value of the ozone demand is chosen in the following way:
i) the value of the residual oxidants and/or dissolved ozone residue desired by the application under consideration for the water to be treated for its final use is known;
ii) the minimum journey time xcex94Tmin between the treatment point and the final user point is evaluated for the application under consideration of the water to be treated;
iii) the persistence of the ozone in the water to be treated is evaluated by measuring, in accordance with stage d) at time intervals after the addition, the content Cf of residual oxidants and/or dissolved ozone in the samples after the addition of Vm;
iv) a level of treatment T is chosen as a function: of the residual oxidants and/or dissolved ozone residue desired by the application under consideration and of the persistence Cf measured during the preceding stage iii) after an interval xcex94Tmin after the addition of Vm.
According to another of the embodiments of the invention, the liquid to be treated is a seawater and successive iterations are then carried out in order to determine the maximum withdrawal volume Vmmax which makes it possible to obtain, immediately after addition, a value of the content Cf substantially identical to that of the content Ci, this being done in the following way:
if Cf is greater than Ci, the stages c) and d) listed above are repeated with a withdrawn portion with a volume of Vn, Vn being less than Vm, until a value of the content Cf is obtained which is substantially identical to that of the content Ci (to within approximately 0.01 mg/l or so);
if Cf is substantially identical to Ci, the stages c) and d) are repeated with a withdrawn portion with a volume of Vn, Vn being greater than Vm, as long as the value of the content Cf is substantially identical to the content Ci (to within approximately 0.01 mg/l or so);
the ozone demand of the water to be treated then corresponds to CmVmmax/Vi (in mg/l);
a level of treatment T equal to the ozone demand is chosen.
According to another of the embodiments of the invention, the water to be treated is a seawater and successive iterations are then carried out in order to determine the maximum withdrawal volume Vmmax which makes it possible to obtain, after a predetermined time xcex94T after the addition, a value of the content Cf substantially identical to that of the content Ci, this being done in the following way:
if Cf is greater than Ci, the stages c) and d) listed above are repeated with a withdrawn portion with a volume of Vn, Vn being less than Vm, until, after the predetermined time xcex94T, a value of the content Cf is obtained which is substantially identical to that of the content Ci (to within approximately 0.01 mg/l or so);
if Cf is substantially identical to Ci, the stages c) and d) are repeated with a withdrawn portion with a volume of Vn, Vn being greater than Vm, as long as the value of the content Cf is, after the predetermined time xcex94T, substantially identical to the content Ci (to within approximately 0.01 mg/l or so);
the ozone demand of the water to be treated then corresponds to CmVmmax/Vi (in mg/l);
a level of treatment T equal to the ozone demand is chosen, and the presence is provided for of a reactor, for holding the water thus treated using the level of treatment T, capable of holding the water thus treated for a time of at least xcex94T, before any subsequent use of the water thus treated.
The present invention also relates to a process for the treatment of a liquid by injection into the liquid to be treated of an ozonized gas employing a level of treatment with ozone T, which is characterized in that the level of treatment T to be applied to the liquid is determined by applying the determination method described above.
According to one of the aspects of the invention, the treatment process is targeted at carrying out one or more of the actions from the following actions; a bleaching, a disinfection or a deodorization of the water, and the liquid thus treated is subsequently used for washing foodstuffs or in aquacultural or pisicicultural rearing sites, rearing sites of the type or all or part of the water which feed the rearing pond or ponds of the user site is treated with ozone.
Other characteristics and advantages of the invention will emerge from the following description, given solely by way of illustration and without implied limitation and made with reference to the appended drawings.